It was found that fibroblasts (L-929, mouse) contain transglutaminase. The proteins that appear to be specific substrates in the cell have been partially purified. It was also demonstrated that fibrinogen could be coupled to the surface of fibroblasts by means of transglutaminase. BIBLIOGRAPHIC REFERENCE: Fesus, L. and Laki, K.: On coupling bovine fibrinogen to the surface of malignant murine plasma cells by means of transglutaminase. Biochem. Biophys. Res. Commun. 72:131-137, 1976.